A known weapon of this type (automatic pistol MP 5 SD) is provided with a silencer capable of reducing the noise of the muzzle blast to a level such that the weapon is superbly suitable for commandos and special missions. Contributing to this quiet operation is the feature that the projectiles, although in the form of conventional ammunition, leave the barrel at subsonic speed so as to avoid the boom that inevitably accompanies the firing of projectiles at supersonic speeds. The reduction in muzzle velocity of the projectiles is achieved by providing the barrel with transverse grooves which terminate in an expansion space sealed off to the outside, whereby the gas pressure is decreased by an amount such that the bullet speed at the muzzle is slightly less than Mach 1. Moreover, this well known weapon has the additional advantage that the breechblock is closed before discharge of the weapon so that there is no sound whatever occurring immediately prior to firing. However, in an automatic weapon, which automatically discards an empty cartridge and feeds the next cartridge from the magazine, it is unavoidable that metallic noises are generated by the relatively rapid breechblock action. Now, there are instances when even this not very loud noise must be avoided because it betrays the presence and the location of the shooter.